C3 (1980) Half-Shafts U-Joint Torque

[David W.]

Hello Guys,

I have had my half-shafts rebuilt on my 1980 C3 and am in the process of installing.
I have the type of u-joint that uses a strap and bolt with 5/16th head. I am confused about the torque specs. My shop manual says 15ft/lbs for the inner u-joint (differential) and 75ft/lbs for the spindle. Is this correct? Why the big difference?
When trying to torque the spindle bolts with the 5/16th head, I stripped 2 due to the position. There seems to be no good way to get to the bolts.
Any suggestions? And should I use locktite on these?

Thanks, David

[Michael G.]

Re: C3 (1980) Half-Shafts U-Joint Torque

David, I believe it is because the spindle flange is just a mated surface connection and requires a tighter connection. The inner universal has a seat and only requires the u-strap to be tight enough to keep it seated.
I don't remember there being any trick to accessing the bolts other than having the rear end supported so that you can rotate the assembly and get full access to each bolt one at a time. Good luck, Mike

[David W.]

Re: C3 (1980) Half-Shafts U-Joint Torque

Mike,

Thanks for the explanation. So, I am still a little confused. The differential yoke mount and spindle mount appear to have the same type of connection/seat to me. What is the difference? I am not sure what a "mated suface" is.
I love this technical stuff and hope you will explain further.
Thanks again and have a happy new year,

David

[Michael G.]

Re: C3 (1980) Half-Shafts U-Joint Torque

David, I'm sorry for the confusion. I forgot that this had changed in 79 . I thought it remained the same through 82'. I assume you have the u-straps at both ends of the half shaft? I was referring to the spindle flange which is attached to the spindle by nut and washer and it's mate, which is pressed onto the outer universal as the shaft was. These two mating pieces make up the spindle flange as they are bolted together. I am at a loss for an explanation for the dramatic difference in torque specs in your configuration. They may have just carried them over from the previous set-up Sorry, Mike

[David W.]

Re: C3 (1980) Half-Shafts U-Joint Torque

Mike,

No problem. Thanks for the info. Why I am confused about the huge difference in torque is.... the u-joints at the end of each half shaft are the same...the mounting surfaces (both spindle and differential yoke) look identical...the straps at either end of the shafts are identical as are the bolts.
So, why the big torque spec difference? The heads of the bolts are 5/16th and trying to torque a 5/16th bolt head to 75ft/lbs in this tight location is trouble. Guess I will need to break out my 1/4 in torque wrench for this job!

Regards, David

[Terry M.]

Re: C3 (1980) Half-Shafts U-Joint Torque

75 foot pounds sounds way too much for a bolt with a 5/16-inch head. That kind of torque will likely strip the threads.

Are both inner and outer bolts the same thread pitch? If one is fine thread and the other course thread it could account for some difference in torque value.

Where are you getting the torque values from? I would suggest you seek other sources for the value and see if they agree. The CSM and AIM would be two sources, but since both are from Chevrolet they might contain the same inaccuracies. Off the top of my head I can't offer a third, independent source, but perhaps someone here might be able to.

[David W.]

Re: C3 (1980) Half-Shafts U-Joint Torque

Terry,

Both inner and outer bolts and straps are the same. On the 1980-82 the spindle flange was different from previous models. The attachment to the spindle uses the same bolts and straps as the attachment to the differential yoke.
I got the torque specs from my shop manual and online. I beleive what has happened is there is no supplement addressing the bolt/strap change vs the earlier models. On a 1979 (and earlier models) I can see where 75ft/lbs could be needed and possible. But, as you say with these smaller 5/16th inch bolt heads, stripping or rounding off of the head is almost guaranteed. The 1st two I tried, both stripped and I had not gotten close to the 75ft/lb goal.
I have seen torque specs vary for the differential yoke to half-shafts but all were in the 15-30 ft/lb range. Again, same bolts and straps that attach to the spindle. Thats why I beleive with the spindle attachment change that began in 1980, the torque should be similar as to the yoke.

Thanks for the input,
David

[John H.]

Re: C3 (1980) Half-Shafts U-Joint Torque

David -

I'm not a C3 guy and don't have any late C3 references, but there's no way on God's green earth that those little 12-point bolts that secure the U-joint straps get 75 ft-lbs. of torque - that's for the four 5/8" hex bolts that attach the outer U-joint FLANGE to the spindle FLANGE.

The exact same 12-point bolts and straps are used on '69 Camaro driveshaft-to-pinion flange U-joint attachment with the 12-bolt axle, and they're spec'd at 12-17 ft-lbs.

[Lynn H.]

Re: C3 (1980) Half-Shafts U-Joint Torque

I have a Haynes manual called an "Owners Workshop Manual" for the Chevrolet Corvette that covers the years 68-82. It list the torque settings for the universal joint straps at 15 lb/ft, or 21 Nm. I think this is the information you are looking for.
Lynn

[David W.]

Re: C3 (1980) Half-Shafts U-Joint Torque

John and Lynn,

Bingo! You guys are right-on! I found my AIM (the one for the 80 model is really bad) and the max is about 32 ft/lbs. Someone needs to update the service manual for the c3's to reflect this. It shows the torque specs for these as 75 ft/lbs. They are not taking into account that the spindal flange was changed after the 79 model.

Regards, David

[Terry M.]

Re: C3 (1980) Half-Shafts U-Joint Torque

In the 1960's, and perhaps other years, it was Chevrolet's practice NOT to update the Service Manuals. Errors were sometimes corrected via Chevrolet Service News, but some errors were never corrected.

I doubt this situation changed too much over the years that paper manuals were the primary documents. Now days the primary service documents are on-line, accessible only to Chevrolet Technicians, and errors MAY be corrected electronically. Even now days, if one buys the paper manuals errors are NOT corrected.

[David H.]

Re: C3 (1980) Half-Shafts U-Joint Torque

John and Lynn,

Bingo! You guys are right-on! I found my AIM (the one for the 80 model is really bad) and the max is about 32 ft/lbs. Someone needs to update the service manual for the c3's to reflect this. It shows the torque specs for these as 75 ft/lbs. They are not taking into account that the spindal flange was changed after the 79 model.

Regards, David

TORQUE READINGS IN THE 1980 AIM ARE IN NEWTON-METERS - NOT FOOT-POUNDS.

First, lightly snug both bolts down - you want about equal gap on both sides of the strap. Then, tighten the bolts for an automatic to 14-20 NM (10 to 15 ft-lbs) - tighten the bolts for a 4 speed to 24-32 NM (18 to 24 ft-lbs).

The 1980 Shop Manual (page 4B-6) shows 16 N-M (140 inch-lbs) for automatics and 28 NM (21 fl-lbs) for 4 speeds.